Antibodies directed against sperm surface antigens are an important contributing factor to "unexplained" infertility in humans. We propose to analyze in detail antibodies to sperm in sera and seminal plasma of individuals with established clinical infertility. We propose to utilize these antibodies to identify antigenic components of sperm relevant to immunologic infertility. The specific experiments are designed to: 1.) analyze by indirect radioimmunoassay for antisperm antibodies a large number of serum and seminal plasma samples obtained from infertile males and evaluate relationships between antibody, immunoglobulin isotype, titer and the clinically defined cause of donor infertility; and 2.) identify by immunochemical and biochemical characterization those components on the surface of human sperm which interact specifically with antibodies to sperm present in sera and seminal plasma from infertile individuals. These studies will provide information important for understanding the role of the sperm surface in reproduction. In addition, they will provide an approach to the development of methods both for the relief of infertility due to the immune response and for the regulation of fertility by immunological means.